1. Field of the Invention
The present invention relates to a method for determining the heading of an aircraft. More particularly, this invention pertains to a method for determining the heading of aircraft equipped with at least one inertial navigation system that includes at least two accelerometers, as well as a device for receiving and processing data obtained from navigation satellites and for computing aircraft position, velocity and acceleration therefrom.
2. Description of the Prior Art
The actual heading of an aircraft equipped with an inertial system has been previously determined either by measuring and processing the (two) horizontal components of the earth's rotation with a gyroscopic compass or by feeding an external heading signal from, for example, a magnetic compass or a radio compass. Highly accurate gyroscopes, not always available (if only for cost reasons) are required to determine heading by measuring the earth's rotation rate. Otherwise, the heading would be insufficiently accurate to meet current aviation requirements where one degree of inaccuracy is the accepted limit.
The utilization of external heading reference signals is generally disadvantageous. When a magnetic probe is used, technical inaccuracies of the measurement due to magnetic disturbance fields caused by electric fields or by iron parts of the vehicle (or carried along) become inadmissibly large. A significant compensation effort is required to keep the basic inaccuracies in the determination of the magnetic deviation due to local deviations within acceptable limits.
In addition to the course above ground (indirectly supplied by the satellite navigation receiver), accurate knowledge of the heading is of considerable importance for various flight operation situations. Such situations occur when calculating wind intensity and direction ("wind vector"), correcting during the landing run on the runway and the like.